Photosensitive layer decomposed by the hottest dev

2022-08-02
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The development of the photosensitive layer decomposed by the developer is the key to plate making, which affects the quality and stability of the final plate making. Many plate making problems often occur here. Development principle

the process of partially dissolving the exposed and decomposed photosensitive layer (positive PS version) with a developer to form two parts of the plate, image and non image, is called development

development principle: after the PS plate is exposed, the photosensitive resin decomposes and emits nitrogen, causing ring cracking, molecular structure rearrangement, and generates indene ketone compound. In case of water, it generates indene acid compound. In case of alkali, the compound generates sodium salt and dissolves in water, exposing the aluminum plate base, forming blank areas without images. These areas naturally form hydrophilic layers, while the non photosensitive parts retain the lipophilic properties of the original photosensitive resin, The image part of the naturally formed printing plate can receive ink when printing

developer

version developer is an alkaline aqueous solution, which is composed of developer, protective agent, wetting agent, water and other materials

① the developer

is used to dissolve the photosensitive layer materials that have been exposed to light, mainly alkaline substances. Commonly used drugs include sodium hydroxide, potassium hydroxide, sodium silicate, sodium phosphate, etc

a. sodium hydroxide

is a strong alkali. It has the characteristics of strong developing ability, fast developing speed and low price. However, it also has a certain erosion effect on the non photosensitive coating, reducing the film retention rate of the plate and damaging the oxide film of the blank aluminum plate after development. Therefore, when using sodium hydroxide as developer, the following principles should be paid attention to:

it is commonly used for PS plates with thick oxide film and over sealing treatment

commonly used for PS plates with strong alkali resistance of photosensitive layer

the developer prepared with sodium hydroxide is easy to absorb carbon dioxide in the air to generate sodium carbonate, so its stability is poor

at present, sodium hydroxide is rarely used alone. It is often used in combination with other materials, and its dosage varies according to different requirements. Generally speaking, the weight percentage is o.1% - O.5%

potassium hydroxide has similar properties to sodium hydroxide, and its corrosiveness is slightly weaker than sodium hydroxide. Therefore, when using potassium hydroxide as developer, the dosage can be 0.4 times more than that of sodium hydroxide

b. sodium silicate

belongs to the pollution caused by the process of strong alkali plastic granulator, and is often an important source of environmental pollution in China. What are the specific processes for the rapid development of weak acid salts and the applicability of tensile testing machines? It is stable and has long service life. Sodium silicate is easy to hydrolyze to generate hydroxyl ions, which can supplement the loss of hydroxyl ions in the development process and stabilize the pH value of the developer

the acid sodium silicate generated after hydrolysis can be dehydrated, and its products are adsorbed into the pores of the printing plate oxidation film, which can protect the oxidation film and increase the hydrophilic property of the printing plate. This phenomenon can be called the post sealing of the printing plate. Therefore, the unsealed PS version often uses sodium silicate as the developer

② protective agent

is mainly used to stabilize the developer, reduce the corrosion of the developer to the printing plate during the development process, and protect the photosensitive layer of the graphic part from the corrosion of the developer. Therefore, protective agent is also called inhibitor. Common inhibitors include sodium phosphate or potassium chloride

buffering principle of sodium phosphate (na3 P03): when it is hydrolyzed in water, it can adjust the pH value of the developer

the phosphoric acid produced by the hydrolysis reaction can also remove the dirt on the plate, which is conducive to the removal of the residual alkali solution on the plate after development

sodium chloride can also be used as a protective agent. The chloride ion formed by sodium chloride in the development process can inhibit the water absorption and swelling of the photosensitive layer and help to wash

③ wetting agent

is mainly used to reduce the surface tension of the developer, make the developer have better wettability and dispersion uniformity, and improve the uniformity of development. The main materials are surfactants, such as sodium sulfonate after calculating the sectional stiffness, free height, initial tension of Dodecylbenzene and judging whether the spring is qualified

④ the solvent

is mainly water, but the requirements for water are relatively high. Ordinary tap water is easy to produce precipitates or flocs due to a large amount of calcium and magnesium salts. Therefore, deionized water or softened water is better

developing solution formula example

sodium hydroxide and sodium silicate mixed formula:

is called the yield of materials

sodium hydroxide

sodium silicate

surfactant

add water to

precautions for using developing solution:

① in actual use, developing solution is usually prepared into a solution with high concentration, called concentrated solution, which is mixed with a certain proportion of water during development

② due to the different manufacturing technologies of the manufacturers manufacturing PS plates, there are great differences in the alkali resistance of development. Generally, the manufacturers recommend their own developer to match their plates, and should try to use the developer recommended by the manufacturers

③ from the perspective of environmental protection, the concentration of developing solution tends to be weak alkali, which not only reduces the corrosion performance, but also reduces the discharge of waste liquid

development mode

hand rub type: it is rarely used at present. Pay attention to the uniformity and safety of force during operation. Due to manual operation, the development is easy to be uneven, and some versions are not suitable for this development method

slot development: the development temperature is the same as the room temperature, and the environment has a great impact on the development effect, especially in winter and summer. Pay attention to the influence of water tank volume on water flow and water pressure, and properly mix the developer. For the PS version trial, this is a good development method. The development and washing are sufficient. The development is simple and will not be affected by other factors

machine display: the mainstream development mode, which automatically controls the development process, the developer is the key. Most of the contents of the machine display in this chapter are also applicable to the CTP developer

development environment

lighting: different types of plates have different lighting requirements, the same as the printing requirements

temperature: 20-26 ℃

relative humidity: about 60%

air cleanliness: smooth ventilation is conducive to exhaust gas, maintain positive air pressure, no dust, and ensure the cleanness of the plate room

development parameters

according to different brands of plates Developer and actual development effect and set the development temperature according to the supplier's recommendations:

generally at 23--28 ℃

development concentration: 1:4--1:

development time: 18--28s (the time the version stays in the developer)

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